Self-capacitance detection technologies are widely used in the field of human-computer interaction of an electronic product, and specifically, a capacitance (a self-capacitance, or a base capacitance) is formed between a detecting electrode and ground, when a conductor (such as a finger) approaches or touches the detecting electrode, the capacitance between the detecting electrode and the ground varies, and information that the conductor approaches or touches the detecting electrode is obtained by detecting an amount of variation in the capacitance.
In some scenarios, for example, a touch screen of a smart phone requires high sensitivity for capacitance detection; for example, a self-capacitance of the detecting electrode to the ground is 1 pF, and when the finger is 30 mm away from the detecting electrode, the self-capacitance of the detecting electrode is increased by 1 fF, that is, signal weight is only 0.1%; in order to extract a useful signal, it is common to use a cancellation circuit to remove a useless signal contributed by a base capacitance of the detecting electrode, that is, 1 pF. However, for a conventional cancellation circuit, there is transient overshoot when driving with a square wave, and an amplitude and a slope of an overshoot voltage are related to parameters of a trace resistance and a parasitic capacitance of the detecting electrode. Therefore, an effective cancellation effect cannot be achieved, and sensitivity of capacitance detection is reduced.
Therefore, a self-capacitance detecting method which can improve the sensitivity of the capacitance detection is required.